In a conventional vehicle control system disclosed in, for instance, US 2006/0041353 (JP 2006-60936A), a required axle torque calculation unit calculates required axle torque which varies depending, for example, upon the amount an accelerator pedal is operated by a driver of a vehicle. The required axle torque calculation unit calculates the required axle torque as the sum of a first axle torque produced by an internal combustion engine and second axle torque produced by an auxiliary machine such as a motor-generator. The required axle torque is used for accelerating or decelerating the vehicle. Here, the required axle torque calculation unit distributes the required axle torque into the first axle torque and the second axle torque in a manner to enhance the energy efficiency depending upon the traveling condition of the vehicle, and the internal combustion engine and the motor-generator produce the thus distributed axle torque.
If the required axle torque calculated by the required axle torque calculation unit is produced by a power plant that includes the internal combustion engine and the auxiliary machine as calculated, the vehicle, in many cases, produces extra energy in excess of energy necessary for realizing the traveling of the vehicle estimated by the driver. The driver tends to require the power plant of the vehicle to produce more power than what is required in order to realize the traveling of the vehicle estimated by the driver himself. Due to the extra power, the vehicle chassis vibrates while the vehicle is traveling as represented by, for example, squat.
To suppress the occurrence of vibration of the vehicle chassis while the vehicle is traveling, therefore, the conventional system is equipped with a pitching vibration correction unit for correcting the axle torque distributed to the auxiliary machine through the required axle torque calculation unit. Specifically, the pitching vibration correction unit calculates the torque input to the vehicle chassis, which is the torque actually produced by the power plant and is input to the vehicle chassis depending upon the amount of the air taken in by the internal combustion engine detected by an intake air amount sensor and an electric current detected by a current sensor that detects the electric current flowing through the auxiliary machine. Next, the pitching vibration correction unit calculates the pitching vibration energy, which corresponds to extra energy, consumed by the occurrence of pitching vibration based upon the calculated torque input to the vehicle chassis and a vibration model on the springs. The pitching vibration correction unit removes the torque corresponding to the pitching vibration energy from the above second axle torque, and drives the auxiliary machine so as to produce the corrected second axle torque. This suppresses the occurrence of pitching vibration of the vehicle chassis.
However, the conventional vehicle control system fails to maintain a storage battery in a favorable condition to supply electric power to various vehicle-mounted devices.
That is, in a condition where a large amount of electric power is needed to drive various vehicle-mounted devices and the amount of the electric power stored in the storage battery is not enough, the auxiliary machine must work as a generator to electrically charge the storage battery. The conventional vehicle control system, however, fails to have the auxiliary machine work to exhibit the function that is needed. Even under the above condition, therefore, the auxiliary machine often works as the motor. As a result, though the pitching vibration can be suppressed from occurring on the vehicle chassis, the electric power stored in the battery becomes in short supply that often causes the operation of the vehicle-mounted devices to lose stability.
The above situation could likewise occur not only when the motor-generator that works as a motor or a generator is used as the auxiliary machine but also when an alternator that works as a generator is used as the auxiliary machine.
When the vehicle is traveling, further, not only the vehicle chassis vibrates but also every part of the vehicle vibrates.